1. Field of the Invention
The present invention relates to a center-electrode assembly and a manufacturing method therefor, a nonreciprocal circuit device and a communication apparatus using the center-electrode assembly.
2. Description of the Related Art
A concentrated-constant-type isolator adapted for use in mobile radio communication apparatuses such as portable telephones generally has the capability of allowing a signal to pass-through in a transmission direction and of obstructing the transmission in the reverse direction.
As such a concentrated-constant-type isolator, an isolator having a structure shown in FIG. 14 is known. The concentrated-constant-type isolator 200 comprises a metallic upper case 250 made from a magnetic metal, a permanent magnet 260, a center-electrode assembly 240, a terminal case 230, a metallic lower case 220 made from a magnetic metal, a spacer 280, a resistance element R, and matching-capacitor elements C11, C12, and C13.
The center-electrode assembly 240 is formed by arranging three center-electrodes 271, 272 and 273, which intersect with each other at an angle of approximately 120°, on the top surface of a microwave ferrite 270, with insulating sheets being interposed therebetween. Ports P1, P2 and P3 at respective ends of these center-electrodes 271, 272 and 273 are bent at a right angle. Furthermore, a common shield 276 which is connected in common to the other ends of the respective center-electrodes 271, 272 and 273 is abutted to the bottom surface of the ferrite 270. The common shield 276 substantially covers the entire bottom surface of the ferrite 270.
The conventional center-electrodes 271, 272 and 273 are made by punching a thin metallic plate. As mentioned above, with the common shield 276 of the plate-like center-electrodes 271, 272 and 273 abutted against the bottom surface of the ferrite 270, the ferrite 270 is wrapped by the center-electrodes 271, 272 and 273, and the three center-electrodes 271, 272 and 273 are bent at right angles at the edges of the ferrite 270. In this connection, there has been a problem that the bending position and the bending angle are unstable according to the shape of the ferrite 270 and the bending conditions (the manner of holding and applying force) when the center-electrodes 271, 272 and 273 are bent.
As a result, the mutual-intersecting angle of the center-electrodes is not stable, which may result in the center-electrodes 240 in different units having different electrical characteristics. In particular, as the shape of the center-electrodes becomes complicated and the center-electrode assembly 240 is miniaturized, the above-mentioned tendency becomes conspicuous. Also, another problems is that the operation of wrapping the ferrite 270 with the plate-like center-electrodes is troublesome and the mass-productivity is low.